1. Field of the Invention
The present invention relates to an image forming apparatus and more particularly to an image forming apparatus capable of performing both a stencil printer type of image formation and a non-stencil printer type of image formation.
2. Description of the Background Art
A digital, thermosensitive stencil printer of the type using a print drum implemented as a porous, hollow cylinder and a stencil is conventional. In this type of printer, a thermal head selectively perforates or cuts the stencil, which is implemented as a laminate of a thermoplastic resin film and a porous support, with heat in accordance with image data to thereby produce a master. After the master has been wrapped around the print drum, ink feeding means arranged inside the print drum feeds an adequate amount of ink to the inner periphery of the print drum. Subsequently, a press roller, press drum or similar pressing member presses a sheet against the print drum via the master. As a result, the ink is transferred to the sheet via the porous portion of the print drum and master. A stencil printer with such a configuration is used mainly to produce as many as several ten or more prints carrying identical image thereon because it reduces cost for a single print and can operate at high speed, i.e., output a great number of prints in a short period of time.
However, a stencil printer, needing a master at the time of printing, is not desirable when only a small number of prints, e.g., one to several prints are desired or when a particular partial image should be printed over each of several ten identical images. Further, when it is desired to print images corresponding to a plurality of different documents with a stencil printer and staple or otherwise bind the resulting prints, collation must be effected after printing. Therefore, a stencil printer is unable to function as, e.g., a copier capable of repeatedly outputting different document images in order of page.
More specifically, a stencil printer or stencil type of image forming apparatus is desirable when a single image should be printed on a great number of sheets. On the other hand, an electrophotographic printer, ink jet printer or similar non-stencil type of image forming apparatus is desirable when different images should be formed on a small number of sheets. While a user, considering such merits and demerits of the two different types of image forming apparatuses, is required to selectively use the apparatuses in accordance with the kind of image formation, the two types of apparatuses would double the cost and space required when installed at the user's station together. Usually, therefore, a user is obliged to own only one of the two types of image forming apparatuses to be used more often than the other.
To solve the problem stated above, Japanese Patent Laid-Open Publication No. 2003-334993, for example, discloses an image forming apparatus including both of a stencil printer section and an ink jet printer or non-stencil printer section and means for moving the ink jet printer section in the widthwise direction of a sheet, which is perpendicular to the direction of sheet conveyance, in accordance with the sheet size. More specifically, the stencil printer section forms an image by using the center of a sheet as a reference while the ink jet printer section forms it by using one edge of a sheet as a reference. In light of this, the means for moving the ink jet printer section mentioned above serves to accurately match the position of an image formed by the stencil printer section (stencil image hereinafter) and that of an image formed by the ink jet printer section (ink jet image or non-stencil image hereinafter) in accordance with the sheet size.
However, Laid-Open Publication No. 2003-334993 mentioned above does not teach any arrangement for shifting the position of the stencil image or that of the ink jet image in the direction of sheet feed or the widthwise direction of a sheet. More specifically, a stencil printer usually includes mechanisms and an operating section for shifting the position of a stencil image relative to a sheet in the direction of sheet conveyance and the widthwise direction of a sheet. By contrast, in the case of an ink jet printer, the position of an ink jet image cannot be shifted relative to a sheet unless it is shifted on a personal computer, which stores image data, by troublesome operation. This indicates that the image forming apparatus taught in the above document is extremely awkward to operate.
Further, it is a common practice to form a plurality of identical images on a single sheet side by side and then cut the sheet to thereby efficiently produce, e.g., a plurality of tickets or cards. In such a case, the image forming apparatus disclosed in Laid-Open Publication No. 2003-334993 is capable of forming identical images by stencil printing and then forming, e.g., addresses or serial numbers in part of the identical images by ink jet printing or non-stencil printing. The prerequisite with this kind of image formation is not only to adequately match the position of the stencil image and that of the non-stencil image, but also to match the distance between nearby non-stencil images to the distance between nearby stencil images. It is extremely difficult to match the above distances with the technology taught in the above document.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 9-104159, 2001-347740 and 2002-127580.